The present invention relates to thrust augmenting devices and more particularly, to an ejector-type engine thrust augmentor.
The device according to the present invention can be used successfully for augmenting engine thrust in aircraft employed, for example, in agricultural aviation.
The invention can also be useful in the jet engines of such transport facilities as hovercraft, railway locomotives, etc.
Known in the previous art is an ejector-type engine thrust augmentor made in the form of an ejector shroud arranged along the flow after the engine nozzle having a circular cross section. The ejector shroud consists of a converging duct, a mixing chamber and a diffuser, all these units are arranged in succession along the flow, and their internal surfaces define the profiled internal surface of the ejector shroud.
The stream of gas of a round cross section discharged from the nozzle of the running engine enters the ejector shroud. The ambient air ejected by this stream enters through a converging duct into the mixing chamber and is mixed with said stream. The mixed flow passes through the diffuser and is ejected out into the atmosphere. These processes of ejection and mixing create additional engine thrust.
A disadvantage of the known ejector-type engine thrust augmentor wherein the thrust is created by ejecting ambient air by the stream of engine gases with a nozzle of a round cross section consists in an excessive length of the mixing chamber of the ejector shroud.
The need for a very long mixing chamber is caused by the insufficiently high ejecting properties of the streams of a round cross section. In case of streams with a round cross section the ejector shroud becomes effective if the length-diameter ratio of the mixing chamber is equal to 5-8.
The employment of such ejector-type thrust augmentors is hampered by their large size and weight. A reduction in the length of the mixing chamber decreases sharply the thrust increment. For example, reducing the chamber length two times causes the thrust increment to drop by more than twice.
When installing the ejector shroud on the aircraft, the dimensions of said shroud must be decreased in the first place by reducing the length of the mixing chamber which is very long in the known design.
Also known in the previous art is a small-size ejector-type thrust augmentor comprising an ejector shroud whose length is equal to one or two diameters of the mixing chamber.
However, such a thrust augmentor can render efficient operation only on the condition that the outlet section of the engine nozzle is not of a conventional round or oval shape but is, for example, star-shaped for increasing the surface of interaction between the ejecting and ejected streams.
However, the engine with a complex-shaped nozzle has but a limited field of employment. Such an engine without an ejector-type thrust augmentor cannot be used in aircraft due to heavy losses of thrust in the complex-shaped nozzle.